Conventionally, in a manufacturing process of a semiconductor device, a processing using a plasma (hereinafter, referred to as “plasma processing”), such as etching or sputtering and CVD (chemical vapor deposition), is performed on a semiconductor wafer (hereinafter, referred to as “wafer”) that is an object to be processed.
For example, as shown in FIG. 8, a plasma processing apparatus 80 for performing an etching process includes a cylindrical vessel 81 for containing a wafer; a susceptor 82 disposed in the cylindrical vessel 81, the susceptor 82 serving as a mounting table on which the wafer is mounted; and pusher pins 83 disposed to penetrate through the susceptor 82 toward a surface thereof on which the wafer is mounted (hereinafter, referred to as “mounting surface”) The susceptor 82 has in the mounting surface an electrostatic chuck 85 in which an electrode connected to a DC power supply 84 is embedded, and a lower electrode 87 connected to a high frequency power supply 86 is provided in the susceptor 82 (see, e.g., Japanese Patent Laid-open Publication No. 5-226291, FIG. 1).
In the plasma processing apparatus 80, once the wafer on the mounting surface is adsorbed to the electrostatic chuck 85 by an electrostatic adsorptive force, a high frequency power is applied to the lower electrode 87 to generate a high frequency electric field between a top surface in the cylindrical vessel 81 and the susceptor 82, so that a processing gas introduced into the cylindrical vessel 81 is dissociated to generate a plasma. The generated plasma is converged to a top surface of the wafer by a focus ring (not shown) disposed to surround the periphery of the wafer to etch an oxide film and the like formed on the top surface of the wafer.
Further, the wafer subject to the etching process is lifted from the mounting surface by the pusher pins 83, and is unloaded out of the cylindrical vessel 81 by a transfer mechanism such as a scalar arm (not shown) moved therein.
From the plasma produced in the etching process, some parts, which are not converged to the top surface of the wafer, collide with an inner wall of the cylindrical vessel to generate particles. Further, during the etching process, there are produced reaction products. Most of these particles and reaction products are discharged out of the cylindrical vessel by using an exhaust unit (not shown), but some of the particles and/or the reaction products remaining in the cylindrical vessel 81 are deposited on the mounting surface. In addition, particles generated from the susceptor 82 due to the plasma and the like are also deposited on the mounting surface. The particles and/or the reaction products deposited on the mounting surface come to be attached as foreign materials to a bottom surface of a wafer when the wafer is mounted on the mounting surface. As a method for removing the particles and/or the reaction products attached to the bottom surface of the wafer, there has been known a wet cleaning using a cleaning fluid and the like.
Further, as a method without using the cleaning fluid, there has been known a removal method wherein a plasma is generated between the wafer lifted by the pusher pins and the mounting surface and the particles on the bottom surface of the wafer are removed by a sputtering action of ions and/or a chemical reaction of radicals in the generated plasma (see, e.g., column 2, line 67 to column 3, line 17 of U.S. Pat. No. 4,962,049).
However, by repeating the wet cleaning, the cleaning fluid is contaminated. Therefore, in the wet cleaning, the top surface of the wafer tends to be contaminated by, e.g., particles contained in the contaminated cleaning fluid. Further, when the wafer that has been subject to the etching process is loaded in a chamber for a next process, the particles remaining on the wafer may contaminate the inside of the chamber.
Moreover, in case of removing the particles on the bottom surface of the wafer by a plasma, the top surface of the wafer suffers damages owing to an excessive plasma processing due to the plasma generated, i.e., the top surface of the wafer is over-etched due to an excessive etching performed thereon.